首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   13121篇
  免费   1397篇
  国内免费   836篇
电工技术   629篇
综合类   1071篇
化学工业   2705篇
金属工艺   356篇
机械仪表   447篇
建筑科学   797篇
矿业工程   393篇
能源动力   573篇
轻工业   1366篇
水利工程   187篇
石油天然气   2873篇
武器工业   60篇
无线电   631篇
一般工业技术   1222篇
冶金工业   669篇
原子能技术   112篇
自动化技术   1263篇
  2024年   75篇
  2023年   239篇
  2022年   370篇
  2021年   447篇
  2020年   546篇
  2019年   527篇
  2018年   426篇
  2017年   497篇
  2016年   493篇
  2015年   518篇
  2014年   778篇
  2013年   1010篇
  2012年   873篇
  2011年   887篇
  2010年   653篇
  2009年   639篇
  2008年   602篇
  2007年   730篇
  2006年   750篇
  2005年   645篇
  2004年   555篇
  2003年   496篇
  2002年   424篇
  2001年   376篇
  2000年   354篇
  1999年   281篇
  1998年   225篇
  1997年   203篇
  1996年   159篇
  1995年   150篇
  1994年   98篇
  1993年   65篇
  1992年   58篇
  1991年   41篇
  1990年   42篇
  1989年   28篇
  1988年   21篇
  1987年   21篇
  1986年   9篇
  1985年   12篇
  1984年   7篇
  1983年   5篇
  1982年   2篇
  1980年   4篇
  1979年   2篇
  1966年   1篇
  1964年   1篇
  1962年   1篇
  1959年   1篇
  1951年   6篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
生物柴油与普通柴油任意比例互溶的混合物可以代替石化柴油供内燃机使用,为了使得这种混合物在内燃机应用中达到好的动力性和排放效果,就需要研究不同比例的生物柴油—柴油混合物的雾化效果。利用数字图像处理的方法对生物柴油-柴油混合物雾化图像进行处理,获得了单位面积内雾化粒度的数量和平均直径,处理速度快捷、准确,减少了传统人工方法分析的主观性和较高的失误率。  相似文献   
102.
介绍了在团粒法工艺的基础上,将尿素熔融成尿液进行喷浆造粒生产复混 肥过程中存在的问题,分析产生的原因并提出改进措施,对改造效果进行了总结。  相似文献   
103.
Walking tracks of Colorado potato beetles,Leptinotarsa decemlineata Say, were recorded on a locomotion-compensator in response to wind, odors of host plantsSolanum tuberosum L. and nonhost plantsLycopersicon hirsutum f.glabratum C.H. Mull, and to mixtures of these plant species. Host-plant odor induced positive anemotactic responses in starved females, whereas odor of the nonhostL. hirsutum was neither repellent nor attractive. The attractiveness of host-plant odor, however, was neutralized in the odor blend of plant species. Masking the attractive host-plant odor will hinder the beetle's searching for host-plant patches, and this principle may be exploited in pest control by mixed cropping.The locomotion-compensator was constructed with financial support from the Foundation for Fundamental Biological Research (BION), which is subsidized by the Netherlands Organization for the Advancement of Pure Research (ZWO), grant 14-02-02. The first author was supported by a grant from the French Ministry of Industry and Research.  相似文献   
104.
The process of grinding soybeans to a fine flour and extracting the flour with hexane was studied on a pilot plant scale. The crude oil from the pilot plant study had 15 ppm phosphorus and was suitable for physical refining after a light acid pretreatment and bleaching. The refined oil showed a Lovibond color of 1.4 yellow and 0.3 red. The pilot plant study also showed that grinding of the soybeans and the separation of solid from miscella were the most difficult steps in solvent extraction with fine flour. A laboratory study on separation of miscella from meal by aqueous ethanol reduced the hold-up volume, but it did not remove all the miscella. A test with betacarotene showed that only the miscella outside the flour particles was displaced. Aqueous ethanol solutions used as a second solvent extracted additional nontriglyceride materials (primarily phospholipids) from the meal. Also, the free fatty acid content of the oil was increased with aqueous ethanol solution wash. The quality of the extracted crude oil was lowered by using a second solvent, but it had the advantage of needing only one centrifugation to separate miscella from meal.  相似文献   
105.
稠油O/W型乳状液稳定性的研究   总被引:1,自引:0,他引:1  
以大庆黑帝庙稠油为研究对象,依据稠油乳化降粘原理及O/W型乳状液的形成机制,考察了表面活性剂类型及添加量,碱的添加量,温度、油/水比、振荡方式等因素对稠油O/W型乳状液稳定性的影响。为筛选降粘剂复合配方及选择降低粘工艺提供了必要的基础数据。  相似文献   
106.
综述化工批处理过程调度建模研究及其实际应用。计划/调度在企业生产管理中起着承上启下的作用,合理的计划调度不但能提高企业的服务水平、降低存储费用,而且还能提高企业的生产能力、加深对过程机制及关键数据的理解。整数规划方法应用于批处理过程计划调度,具有较好的适用性和扩展性,解的性质良好,在批处理过程调度研究得到广泛的应用。  相似文献   
107.
New silane monomers with the pendant 4-(3-pyridine)butyl group have been synthesized by hydrosilation of 3-(3-butenyl)pyridine with Me n Si(OEt)3-n H (n=0, 1) using a platinum catalyst. Only -addition products were observed. The products were characterized by elemental analysis, infrared,1H- and13C-NMR spectroscopy, and gas chromatography-mass spectrometry. Hydrolysis-polycondensation of the difunctional monomer with a basic catalyst, Me4NOH, gave a mixture of cyclic oligomers, principally cyclic tetramer, and linear homopolymer. Under similar reaction conditions, the trifunctional monomer gave crosslinked material which was soluble in common organic solvents. The linear homopolymer and crosslinked polymer were trimethylsilyl end-blocked with hexamethyldisilazane. The cyclic and end-blocked polymers were characterized by elemental analysis and spectroscopic methods. Molecular weights of the polymers were obtained by end-group analysis using1H-NMR spectral data, size exclusion chromatography, and direct insertion-probe mass spectrometry. The cyclic, linear, and crosslinked materials were N-oxidized withm-chloroperoxybenzoic acid and characterized by spectroscopic methods. The polymeric N-oxide derivatives were shown to be effective transacylation catalysts in the synthesis of mixed carboxylic acid anhydrides in immiscible solvents (H2O/CH2Cl2) under phase-transfer conditions. The implications of the results on the mechanism of catalysis are discussed.  相似文献   
108.
Dry reforming of methane has been investigated on two series of catalysts either prepared by co-precipitation: n(NixMgy)/Al, NixMgy and NixAly or prepared by impregnation: Ni/MgO (mol% Ni = 5, 10). The catalysts, calcined at 600–900 °C, were characterized by different techniques: BET, H2-TPR, TPO, XRD, IR, and TEM-EDX analysis. The surface BET (30–182 m2 g−1) decreased with increasing the temperature of calcination, after reduction and in the presence of Mg element. The XRD analysis showed, for n(NixMgy)/Al catalysts, the presence of NiAl2O4 and NiO–MgO solid solutions. The catalyst reducibility decreased with increasing the temperature of pretreatment. The n(NixMgy)/Al catalysts were active for dry reforming of methane with a good resistance to coke formation. The bimetallic catalyst Ni0.05Mg0.95 (calcined at 750 °C and tested at 800 °C) presents a poor activity. In contrast, the 5% Ni/MgO catalyst, having the same composition but prepared by impregnation, presents a high activity for the same calcination and reaction conditions. For all the catalysts the activity decreased with increasing the temperature of calcination and a previous H2-reduction of the catalyst improves the performances. The TPO profiles and TEM-EDX analysis showed mainly four types of coke: CHx species, surface carbon, nickel carbide and carbon nanotubes.  相似文献   
109.
The effect of preparation method on MnO x –CeO2 mixed oxide catalysts for methane combustion at low temperature was investigated by means of BET, XRD, XPS, H2-TPR techniques and methane oxidation reaction. The catalysts were prepared by the conventional coprecipitation, plasma and modified coprecipitation methods, respectively. It was found that the catalyst prepared by modified coprecipitation was the most active, over which methane conversion reached 90% at a temperature as low as 390 °C. The XRD results showed the preparation methods had no effect on the solid solution structure of MnO x –CeO2 catalysts. More Mn4+ and richer lattice oxygen were found on the surface of the modified coprecipitation prepared catalyst with the help of XPS analysis, and its reduction and BET surface area were remarkably promoted. These factors could be responsible for its higher activity for methane combustion at low temperature.  相似文献   
110.
针对混凝土小型空心砌块的特点,配制出专用混合砂浆.该砂浆未添加外加剂,便于建筑施工.实验结果表明该混合砂浆和易性能良好.该配合比可以作为基准配合比供其它工程借鉴、使用.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号